REUTERS - The United States on Thursday called on Israel to do more to prevent Palestinian civilian casualties in its conflict with Hamas militants after four children were killed on a beach in the Gaza Strip.

Even while stepping up U.S. pressure for Israeli restraint, State Department spokeswoman Jen Psaki reasserted Washington’s condemnation of Hamas’s “indiscriminate rocket attacks” targeting Israeli civilians and affirmed U.S. support for Israel’s right to defend itself.

“We continue to urge all parties to do all they can to protect civilians,” she told reporters at the State Department’s daily briefing. “We have been heart-broken by the high civilian death toll in Gaza.”

U.S. Secretary of State John Kerry underscored in a telephone call with Israeli Prime Minister Benjamin Netanyahu on Wednesday that “there’s more that can be done” by Israel to avoid civilian casualties and that it must redouble its efforts, Psaki said.

According to the State Department, in their conversation, Kerry emphasized the need to avoid further escalation and to restore the 2012 cease-fire as soon as possible, reinforced our continuing commitment to the Egyptian initiative as the way to do so, and underscored the importance of Hamas accepting this plan as soon as possible.

Kerry accepted Netanyahu's explanation that the operation is meant to deal with the threat emanating from Hamas' tunnels in Gaza into Israel, and expressed the U.S.'s view that this should be a precise operation to target tunnels.

An Israeli gunboat off Gaza's Mediterranean coast shelled a Gaza beach on Wednesday, killing four boys - two aged 10 and the others 9 and 11 - from one family and critically wounding another youngster, according to witnesses and a Gaza Health Ministry official.

The Israeli military said it targeted Hamas operatives but that the reported civilian casualties were unintended and tragic and it was investigating. Israel has long accused militants of storing weapons in civilian facilities and using Gaza residents as human shields by launching rockets from residential areas.

“The tragic event makes clear that Israel must take every possible step to meet its standards for protecting civilians from being killed," Psaki said.

Psaki also said: “I don't think we've made any secret about our concern, strong concern about the actions of Hamas, the indiscriminate rocket attacks, the targeting of civilians - and that concern remains.”

She spoke just hours before an official statement from Netanyahu’s office instructed the military to begin a ground operation “to hit the terror tunnels from Gaza into Israel.”

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